1. Field of the Invention
This invention relates to the use of modifiers based on ethylenes or amorphous olefin elastomers for reducing the surface tack of amorphous polypropylenes.
2. Prior Art
Soft, predominantly or completely thermoplastic polyolefins are of great interest, both technically and commercially. Specifically highly amorphous polypropylenes, as known from, for example, EP-A-632062 (PCD Polymere GmbH) or EP-A-475307 (REXENE Corp.), have behavior which diverges markedly from that of conventional isotactic polypropylene. Their particular features are softness, elasticity and impact strength coupled with substantial retention of the relatively high melting point which is an inherent advantage of polypropylene (PP). This combined with the chemical makeup of the material (it is chemically inert and a pure polyolefin, containing neither halogens nor plasticizers, and therefore has extremely good environmental compatibility) opens up application sectors which are new and not hitherto accessible to PP, for example replacement of plasticized PVC or of thermoplastic elastomers.
However, these materials often have a degree of surface tack, which is felt to be a problem or hindrance in a large number of applications. The surface deposit is formed when, for example, components which increase gloss or opacity and, in addition, are tacky bleed out onto the surface of, for example, moldings or films made from materials of this type, either when they are being processed or subsequently when the parts are stored. Efforts have therefore been made to find ways of preventing this process by subsequent modification without altering the production process, and while maintaining the property profile as substantially as possible. For example, in WO 96/22327 PP a very complicated grafting process is used to reduce tack, and JP-Kokai 90/48882 and JP-Kokai 80/67779 on the one hand and DE-A 2127709 on the other mixing with styrene elastomers and organic additives, respectively. These known processes, however, are in some respects very complicated and result in only unsatisfactory or inadequate reduction in surface tack.